Ten years ago, Miami-Dade owed about $100 in property-tax debt for every resident in the county. Now that obligation is closer to $475 per resident.

The figures offer a personal look at the growing amount of county debt backed by Miami-Dade property taxes — obligations that now top $1.4 billion. Published each year in the county’s report to bond holders, the debt-per-resident ratio shows how much it would cost each resident to pay off all of the property-tax debt. That theoretical tab has increased about 375 percent in 10 years, according to the latest numbers from Miami-Dade.

Voters must approve borrowing against property taxes, and Miami-Dade has a special countywide property tax for those obligations. It currently costs $45 for every $100,000 of a property’s taxable value.

Almost all of the new property-tax debt comes from the Building Better Communities bond initiative, a $2.9 billion borrowing plan that voters approved in 2004 to build museums, repair roads and bridges, expand police and court facilities and fund hundreds of other construction projects.

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Miami-Dade has borrowed about 45 percent of the authorized BBC money — roughly $1.3 billion, according to the 2015 budget. But it has paid back less than 5 percent of it — roughly $58 million.

That’s thanks to an amortization schedule that pushes most of the principal repayment into later years. This is similar to how most homeowners pay off mortgages, but with the difference that Miami-Dade continues making new loans to fund more BBC projects.

The result: debt that’s been growing quickly, while the population expands at a far more modest rate. (The bond office notes none of this should be a surprise. In 2004, the $2.9 billion BBC debt that voters approved amounted to about $1,230 in debt per resident.)

Our Dade Data chart tracks a resident’s share of property-tax debt through 2013, the most recent year available in the county’s bond books. It also shows the overall property-tax debt for Miami-Dade. [Don’t see a chart? Click here for a link.]

In 2013, property-tax debt stood at $1.2 billion, and the obligation amounted to $477 per resident in a county with a population around 2.5 million, according to the county’s bond office.

In 2003, property-tax debt totaled about $240 million. That amounted to roughly $103 per resident when the population was closer to 2.3 million. (The county’s bond book had a slightly lower figure for 2013, but the office that puts out the book provided updated numbers this week.)

Miami-Dade’s debt-to-resident ratio has no purpose beyond a mathematical exercise. County residents have no obligation to pay back county debt.

But the numbers behind the trend have real consequences. With debt growing, the special property tax that funds voter-approved borrowing has also soared. The 2015 rate of $45 per $100,000 of a property’s value is up almost 60 percent from where it was a decade ago, and it is set to grow another 50 percent in 2016, according to county forecasts.

Both the debt tax and the debt-per-resident ratio are tied to the same liability: the $1.4 billion Miami-Dade is paying back with its special property tax for debt. Property-tax debt is officially called general obligation debt, because the county is essentially pledged to raise property taxes enough to pay for it.

The debt-to-resident ratio divides up the entire obligation by the number of people in the county. But the debt tax basically chops up the annual debt payment (principal plus interest) and distributes it according to each property’s share of the county’s overall tax roll.

(How the numbers work: A house with a taxable value of $200,000 represents about .0001 percent of the county’s $210 billion tax roll. The $90 debt-tax bill for that house also represents about .0001 percent of the $89 million that budget documents show Miami-Dade will pay in principal and interest this year on its $1.4 billion in general-obligation debt.)

Miami-Dade’s $1.4 billion worth of general-obligation debt is a fraction of the county’s entire liabilities, which total more than $16 billion, according to the latest report. But most of that $16 billion is tied to projects at county departments with their own revenue sources for debt — such as Miami International Airport, which borrows against airline fees, or the county sewage system, which uses revenue from water bills to fund infrastructure borrowing.

This post is part of Dade Data, an online series from the Miami Herald’s County Hall team. Dade Data explores the numbers driving Miami-Dade County’s government.